The present invention generally relates to liquid treatment systems, and more particularly to the use and operation of a liquid treatment system designed to effectively remove dissolved metals from liquid compositions.
Industrial, mining, agricultural, and various natural processes often produce considerable amounts of waste water. This water is frequently contaminated with a variety of undesirable materials ranging from organic solvents to heavy metal ions. The removal of dissolved metals (e.g. metal ions) from water is of particular importance, especially with respect to ions of the following metals: group II(A) metals, transition metals (e.g. including but not limited to nickel, copper, cobalt, zinc, cadmium, iron, manganese, chromium, and silver), group III(A) metals (e.g. thallium), group IV(A) metals (e.g. lead), as well as various metalloids/semimetals within groups V(A) and VI(A) including but not limited to arsenic and selenium. These materials may present considerable environmental and toxicity problems. Thus, it is important that they be removed from waste water in an efficient manner and disposed of properly.
In addition, as described in greater detail below, many mining processes including but not limited to procedures associated with copper production involve materials known as "lixivants" which are used to leach metals (e.g. copper ions) from ore. Exemplary lixivants suitable for use in copper production preferably include a strong acid therein (e.g. H.sub.2 SO.sub.4). As the lixivant solution passes downwardly through a heap or pile of copper ore, a liquid product is produced which contains remaining amounts of acid in combination with copper ions. These copper ions must then be removed from the liquid product to produce a copper ion concentrate. The copper ion concentrate is subsequently treated using a selected process (including but not limited to solvent extraction/electrowinning ("SX/EW") as described in greater detail below) to obtain metallic copper. It is therefore important to remove metal ions from the liquid product in the most complete and effective manner possible so that economic benefits of the entire mining process may be maximized.
Many chemical and physical techniques have been developed for removing dissolved metals (e.g. metal ions) from liquids. For example, as described in Ying, Wei-Chi, et. al., "Precipitation Treatment of Spent Electroless Nickel Plating Baths", Journal of Hazardous Materials, 18:69-89 (1988), one procedure involves the precipitation of metal ions with caustic soda or lime. In the alternative, one recently-developed, highly efficient technique involves the use of polymer materials (preferably in the form of beads or other small units) having metal ion extracting agents therein. These materials are described in U.S. Pat. No. 5,279,745 to Jeffers et al. which is incorporated herein by reference. They specifically involve polymeric beads made of polysulfone, cellulose acetate, or other organic polymers having various metal ion extracting agents therein. Exemplary metal ion extracting agents include but are not limited to selected biomass materials (e.g. peat moss, yeast, algae, molds, xanthan gum, guar gum, alginates, and mixtures thereof). Other extracting agents include but are not limited to triisooctyl amine, di-2-ethylhexyl phosphoric acid, tri-octyl methylammonium chloride, 2-hydroxy-5-dodecyl-benzophenone oxime, and di-2-4,4-trimethylpentyl phosphinic acid.
Exemplary bead materials are prepared by first dissolving high-density polysulfone in an organic solvent known in the art (e.g. dimethylformamide [DMF]). Next, the desired biomass materials or chemical extractants are mixed with the polysulfone-DMF mixture. To facilitate this procedure, the biomass/extractants may first be adsorbed onto activated carbon.
After this step, inert metal powders (e.g. magnetite) may be combined with the mixture to increase bead density and/or impart magnetic properties to the beads. Finally, the mixture is injected through a nozzle into water, whereby porous, spherical beads preferably ranging in size from about 1/64 to 1/4 inches in diameter are immediately produced. The beads have a relatively intricate internal pore structure, with the biomass/extractants being immobilized/entrained therein. It is preferred that the beads be fabricated from mixtures containing about 75-200 g of polysulfone per liter of solvent. It is also preferred that polar solvents be used to produce the beads, and other representative solvents which may be used include but are not limited to dimethyl sulfoxide, tetrahydrofuran, acetone, and mixtures thereof. Other biomass materials of interest include penicillium mold and common duckweed (Lemna sp.)
The polymeric units e.g. beads) described herein are highly efficient in removing dissolved metals (e.g. metal ions) from liquids. Specifically, dissolved metals in the selected liquids flow into the internal pore structures of the polymeric units where they are retained therein by the biomass materials/chemical extractants. However, in order to efficiently use the polymeric units for large scale treatment purposes, they must be periodically "regenerated". Regeneration (e.g. cleaning) involves the removal of collected metals from the polymeric units so that they may be reused.
The present invention specifically provides an improved method for liquid treatment in which a rapid and efficient procedure is disclosed for removing metal ions from liquid materials. Accordingly, the invention represents an advance in the art of liquid treatment technology, as described in detail herein.